Question

A train sounds its horn as it approaches an intersection. The horn
can just be heard at a level of 40 dB by an observer 10 km
away.
(a) What is the average power generated by the horn?
(b) What intensity level of the horn's sound is observed by someone
waiting at an intersection 52 m from the train? Treat the horn as a
point source and neglect any absorption of sound by the air.